Office of Governor Rick Snyder(LANSING, Mich.) -- Michigan's republican-controlled state legislature approved a controversial right-to-work bill Tuesday by a vote of 58-51. The bill now moves to Republican Governor Rick Snyder's desk, where he is expected to sign it into law.

Michigan’s law would make the payment of union dues voluntary for private-sector unions and most public-sector unions (police and firefighters would be exempt). In anticipation of the vote, tens of thousands of protesters have descended upon the state capitol in Lansing, demonstrating their opposition to the bill both inside and outside the capital building.

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At noon, demonstrations moved to the governor's main office -- officially titled the Romney building, after former Michigan governor (and father of Mitt) George Romney. Demonstrators engaged in what labor officials termed "peaceful civil disobedience" -- linking arms to block entrances, chanting, and singing.

During his governorship George Romney signed the first bills in the state, which gave collective bargaining rights to public sector employees into law.

If Snyder signs the bill Tuesday, it will still be possible to put it on the ballot in 2014, when Snyder will be running for re-election. The bill includes appropriations, which means that it will automatically become law and will be implemented if signed, but the state constitution allows for voters to invoke a referendum to "approve or reject" the law.

In order to get this referendum on the ballot, opponents of the law will have 90 days after the legislature adjourns to gather 8 percent of the total votes cast in the last gubernatorial race, which was over 3 million. If they succeed, the law will be placed on the ballot and subject to a statewide vote.